Gas-tight bushing with gas filling and control electrodes



Feb. 8, 1966 E. A. FRowl-:IN

GAS-TIGHT BUSHING WITH GAS FILLING AND CONTROL ELEGTRODES Filed oct. e, 196s INVENTOR Egberzus Adr/'an us Frome n m' j XgAI/TOORAIEYS;

United States Patent O 3,234,322 GAS-TEGHT' BUSHlNG WHTH GAS FELMNG AND CNTRUL ELECTRODES Egbertus Adrianus Frowein, Nusshaumen, Switzerland, assigner to Aktiengesellschaft Brown, Roveri d: Cie, Baden, Switzerland, a joint-stock company Filed Oct. 8, 1963, Ser. No. 314,796 Claims priority, application Switzerland, Nov. 23, 1962, 13,790/ 62 2 Claims. (Cl. 174-143) The present invention lrelates to an improvement in gas-tight bushings lilled with a gas and which include control electrodes. Such bushings are utilized as a leadthrough for electrical conductors carrying a relatively high voltage in order to insulate the conductor at the lead-through point of the conductor from a casing or the like containing electrical equipment, and the control electrodes are used for controlling the voltage gradient within the bushing.

-In the past it has been proposed to position the metallic control electrodes in the walls of the insulator housing which forms the body of the bushing at the same time the latter is cast, the casting material usually being a suitable resin. However, it has been observed that when large electrodes are required within the bushing, undesirable cavities are formed between the metal and the cast resin due t-o the different temperature coetiicients of the resin and metal.

The object of the present invention is to provide an improved bushing construction by -which the formation of such cavities betwen the metallic electrodes and the resin walls of the insulator body is avoided, this objective being attained by the use of internally threaded rings positioned centrally within the bushing and whichy are fixed partially within the inside wall of the bushing at the time the latter is cast from its resinous composition, the rings extending into the inside wall only so far as the beginning of the internal curvature thereof, i.e. only so far as the location of internal threads. The control electrodes are then screwed onto these rings.

The invention will become more apparent from the toll-owing detailed description of one suitable embodiment and trom the accompanying drawing which illustrates the same. The drawing is :a central vertical section through the bushing which is a -figure of revolution about the axis of the electrical `conductor which is passed through it.

With reference now to the drawing, it will be seen that the round housing or body portion ot the bushing indicated at 1 has a step-like tapered configuration with the smallest diameter at the upper end 1a. This body portion is moulded from a casting resin of `suitable composition and the upper end of the conductor rod 5 which passes axially through the hollow interior of the body 1 lis provided with axially spaced flanges `5a which are cast in, so to speak, in the upper end la of the resin body at the same time the latter is moulded. The lower end 5b of the conductor rod 5 is set into a cast resin positioning cap 2 which, in turn, is detachable. The external diameter of cap 2 is only a few tenths of a millimeter less than the internal diameter of a flange 6 having a cylindrical portion 6a which likewise is secured within the lower end 1b of body 1 at the time the latter is moulded. The liange 6 serves to secure the complete bushing onto a casing 7 or other structure into which the conductor rod 5 extends.

Positioning rings 3 are located concentrically within the body 1 for supporting the control electrodes 4. Two such rings lare utilized in the illustrated embodiment, these being located one above the other, and they are likewise ICC cast in, so to speak, in position partially within a cylindrical portion of the inside wall of the body 1 at the same time the latter is moulded. It will be noted that the rings 3 extend into the inside wall only so ffar as the curved portions 3b of the rings `begin and that these curved portions -are thus not encased within the resin. These curved portions 3b begin at a diameter substantially coincident with the internally threaded portions 3a of the rings onto which the upper, male threaded ends 4a of the electrodes 4 are screwed. The rings 3 and electrodes 4 are stepped in diameter and surround the conductor rod 5 concentrically. Formation of cavities between the rings 3 and the walls or the body l. during moulding of the latter as well as afterwards, d-uring cooling, is avoided. During cooling, radially inward shrinkage of the cast resin body 1 exceeds a similar shrinkage of ring 3 due to the tact that the 'coetilcient of expansion of the casting resin is larger than that of 4the metal which may, for example, be iron. However, notwithstanding the higher shrinkage characteristic ot the cast resin, the ring contiguration is such that the inner wall of the resin body 1 does not shrink radially inward beyond the point 3b on the ring where the inner curved part of the ring begin-s, and this avoids creation of -any gaps at this crit-ical point with their attendant undesirable electrical stress characteristics.

In addition to the prevention of undesirable cavities between metal and casting resin, the invention offers the further advantage that the control electrodes are insert- -able and removable simply by a screw connection, a tact which makes the construction, and later, the servicing of the bushing easier. Manufacture of the insulating body trom casting resin is also made easier and hence less expensive.

A suitable material for the casting resin which forms the moulded body 1 of the bushing is a mixture of -lVs resin such as, tor example, `a resin available under the trade name Araldite B and LA quartz.

I claim:

1. ln a hollow gas-tight bushing adapted to be filled with gas and having an electrical conductor rod passed therethrough, the improvement wherein said bushing is a cast resin and includes within the same at least one castin internally threaded metallic ring concentric with said conductor rod and surrounding the latter, said ring including a radially inner curved portion and being partially embedded within a cylindrical part of the inner wall of said bushing body but only up -to the point where said radially inner curved yportion begins as a result of radially inward shrinkage attributable to `cooling after casting, and a metallic control electrode surrounding said conductor rod in the space between said rod and said inner wall of said bushing, said control electrode having an externally threaded portion screwed onto the internal threaded portion of said ring.

2. A bushing structure as defined in claim 1 wherein a plurality of said rings and attached control electrodes are included within said bushing body, said rings and electrodes being stepped in diameter to match stepped diameter portion-s of said bushing body, and said electrodes being located in partially telescoped relation.

References Cited bythe Examiner UNITED STATES PATENTS 2,358,553 9/1944 Beldi 174--142 X FOREIGN PATENTS 394,787 5/ 1924 Germany.

JOHN F. BURNS, Primary Examiner.

LARAMIE E. ASKIN, Examiner. 

1. IN A HOLLOW GAS-TIGHT BUSHING ADAPTED TO BE FILLED WITH GAS AND HAVING AN ELECTRICAL CONDUCTOR ROD PASSED THERETHROUGH, THE IMPROVEMENT WHEREIN SAID BUSHING IS A CAST RESIN AND INCLUDES WITHIN THE SAME AT LEAST ONE CASTIN INTERNALLY THREADED METALLIC RING CONCENTRIC WITH SAID CONDUCTOR ROD AND SURROUNDING THE LATTER, SAID RING INCLUDING A RADIALLY INNER CURVED PORTION AND BEING PARTIALLY EMBEDDED WITHIN A CYLINDRICAL PART OF THE INNER WALL OF SAID BUSHING BODY BUT ONLY UP TO THE POINT WHERE SAID RADIALLY INNER CURVED PORTION BEGINS AS A RESULT OF RADIALLY INWARD SHRINKAGE ATTRIBUTABLE TO COOLING AFTER CASTING, AND A METALLIC CONTROL ELECTRODE SURROUNDING SAID CONDUCTOR ROD IN THE SPACE BETWEEN SAID ROD AND SAID INNER WALL OF SAID BUSHING, SAID CONTROL ELECTRODE HAVING AN EXTERNALLY THREADED PORTION SCREWED ONTO THE INTERNAL THREADED PORTION OF SAID RING. 